Gravure cylinders are used for coating liquid compositions on moving supports. The amount of liquid deposited by the gravure cylinder is a function of the recessed cells on the surface of the cylinder. A typical design used in an engraving for the gravure cylinder has been reliance on a large inventory of finished cylinders having different engraved cell patterns, sizes and shapes. The proper lay down of the liquid coating composition is determined empirically, by either trying a number of cylinders, or using cylinders that worked previously. Although somewhat successful, the shortcomings of this method are the reliance upon empirical experimentation and the ability of a single source engraver service to make it "like another cylinder." The engraver would empirically change the cell depth to increase or decrease fluid deposit lay down with a minimum concern for cell geometry effect on coating quality.
U.S. Pat. No. 5,426,588, hereby incorporated herein by reference, discloses a process of electromechanical engraving and a method for specifying cell geometry and engraving process setup conditions based on a cell volume model. In accordance with the aforementioned method, a skilled artisan can specify to an engraver the proper parameters needed to engrave a cylinder that will produce the desired coating coverage. Using these guidelines it is possible to specify an engraving process that will yield good coating quality for formulations which do not contain particulate material, such as beads. However, when gravure coatings containing particulate materials are used in low gloss printing applications, the method described in U.S. Pat. No. 5,426,588 is not sufficient to predict acceptable coating or imaging performance.
A particular problem with coating formulations containing particles, such as beads, which are dispersed but not dissolved in the formulation is that the particles can interact with the engraving process in such a manner that the expected good coating quality is not achieved. One such coating formulation is disclosed in Japanese Kokai [1997]-323482. According to this Japanese Kokai, the use of imaging-protecting layers that contain thermally expandable micro-capsules for "easy matting" of the image surface are described. When micro-capsules such as these are used a more severe problem can occur in gravure coated image protecting layers where an objectionable image artifact can be observed based on an interference pattern which results when the light source orientation and the coating direction of the protecting layer coincide. This artifact can be eliminated and the gloss position can be improved by specifically defining the engraving dimensions for the gravure cylinder with respect to the particle size range being used in the formulation.
Therefore, there exists a need in the art for a modified method for specifying engraving parameters which takes into account the specific size range of the beads or particles that are in the coating formulation.